20 research outputs found
The role of gravitational instabilities in deposition of volcanic ash
Volcanic ash is a significant hazard for areas close to volcanoes and for aviation. Gravitational instabilities forming at the bottom of spreading volcanic clouds have been observed in many explosive eruptions. Here we present the first quantitative description of the dynamics of such instabilities, and correlate this with the characteristics of the fall deposit from observations of the 4 May 2010 Eyjafjallajökull (Iceland) eruption. Gravitational instabilities initially took the form of downward-propagating fingers that formed continuously at the base of the cloud, and appeared to be advected passively at the crosswind speed. Measurements of finger propagation are consistent with initial conditions inferred from previous studies of ash cloud dynamics. Dedicated laboratory analogue experiments confirmed that finger downward propagation significantly exceeded the settling speed of individual particles, demonstrating that gravitational instabilities provide a possible mechanism for enhanced sedimentation of fine ash. Our observations challenge the view that aggregation is the primary explanation of proximal fine ash sedimentation, and give direct support for the role of gravitational instabilities in providing regions of high particle concentration that can promote aggregation
Late HIV Diagnosis and Determinants of Progression to AIDS or Death after HIV Diagnosis among Injection Drug Users, 33 US States, 1996â2004
BACKGROUND: The timeliness of HIV diagnosis and the initiation of antiretroviral treatment are major determinants of survival for HIV-infected people. Injection drug users (IDUs) are less likely than persons in other transmission categories to seek early HIV counseling, testing, and treatment. Our objective was to estimate the proportion of IDUs with a late HIV diagnosis (AIDS diagnosis within 12 months of HIV diagnosis) and determine the factors associated with disease progression after HIV diagnosis. METHODOLOGY/PRINCIPAL FINDINGS: Using data from 33 states with confidential name-based HIV reporting, we determined the proportion of IDUs aged >or=13 years who received a late HIV diagnosis during 1996-2004. We used standardized Kaplan-Meier survival methods to determine differences in time of progression from HIV to AIDS and death, by race/ethnicity, sex, age group, CD4(+) T-cell count, metropolitan residence, and diagnosis year. We compared the survival of IDUs with the survival of persons in other transmission categories. During 1996-2004, 42.2% (11,635) of 27,572 IDUs were diagnosed late. For IDUs, the risk for progression from HIV to AIDS 3 years after HIV diagnosis was greater for nonwhites, males and older persons. Three-year survival after HIV diagnosis was lower for IDU males (87.3%, 95% confidence interval (CI), 87.1-87.4) compared with males exposed through male-to-male sexual contact (91.6%, 95% CI, 91.6-91.7) and males exposed through high-risk heterosexual contact (HRHC) (91.9%, 95% CI, 91.8-91.9). Survival was also lower for IDU females (89.5%, 95% CI, 89.4-89.6) compared to HRHC females (93.3%, 95% CI, 93.3-93.4). CONCLUSIONS/SIGNIFICANCE: A substantial proportion of IDUs living with HIV received their HIV diagnosis late. To improve survival of IDUs, HIV prevention efforts must ensure early access to HIV testing and care, as well as encourage adherence to antiretroviral treatment to slow disease progression
A EDUCAĂĂO CIENTĂFICA COMO ELEMENTO DE DESENVOLVIMENTO HUMANO: UMA PERSPECTIVA DE CONSTRUĂĂO DISCURSIVA
Settling-driven gravitational instabilities associated with volcanic clouds: new insights from experimental investigations
Downward propagating instabilities are often observed
at the bottom of volcanic plumes and clouds. These
instabilities generate fingers that enhance the sedimentation of
fine ash. Despite their potential influence on tephra dispersal
and deposition, their dynamics is not entirely understood,
undermining the accuracy of volcanic ash transport and dispersal
models. Here, we present new laboratory experiments
that investigate the effects of particle size, composition and
concentration on finger generation and dynamics. The experimental
set-up consists of a Plexiglas tank equipped with a
removable plastic sheet that separates two different layers.
The lower layer is a solution of water and sugar, initially
denser than the upper layer, which consists of water and particles.
Particles in the experiments include glass beads as well
as andesitic, rhyolitic and basaltic volcanic ash. During the
experiments, we removed the horizontal plastic sheet separating
the two fluids. Particles were illuminated with a laser and
filmed with a HD camera; particle image velocimetry (PIV) is
used to analyse finger dynamics. Results show that both the
number and the downward advance speed of fingers increase
with particle concentration in the upper layer, while finger
speed increases with particle size but is independent of particle
composition. An increase in particle concentration and turbulence
is estimated to take place inside the fingers, which could
promote aggregation in subaerial fallout events. Finally, finger
number, finger speed and particle concentration were observed
to decrease with time after the formation of fingers.
A similar pattern could occur in volcanic clouds when the
mass supply from the eruptive vent is reduced. Observed evolution
of the experiments through time also indicates that there
must be a threshold of fine ash concentration and mass eruption
rate below which fingers do not form; this is also confirmed
by field observations.Published395V. Dinamica dei processi eruttivi e post-eruttiviJCR Journa
Giving mothers a voice: towards home involvement in high school science
Parents, in particular mothers, often have little knowledge of or confidence in science, yet their involvement and interest in their childrenâs school work can have a positive effect on their childrenâs choice of subjects for study or their future career. At the high school level, parental involvement can be particularly problematic. This paper describes a pilot programme which was designed to engage mothers in the kind of science that their children would encounter in high school, to encourage greater confidence in their science knowledge and experience. It was envisaged that this would, in its turn, facilitate conversations about science between these women and their teenage children. A constructivist, hands-on approach to learning, using easily available materials, ensured that most activities could be repeated in the home environment. The approach was gender-specific and culturally appropriate to the age group. Seventeen mothers attended the programme over six mornings. Evaluations indicate that there was a range of positive outcomes, particularly in the reported level of parentâchild discussions. There is a necessity for further research, however, to investigate the effect on the students, to encompass a broader participant demographic, and achieve a transferable model
Survival of persons with HIV<sup>*</sup> diagnosis by transmission category in 1996â2004, 33 U.S. States.
*<p>Diagnosis of HIV infection with or without a concurrent diagnosis of AIDS.</p
Survival of IDUs with HIV<sup>*</sup> diagnosis in 1996â2004, 33 U.S. States.
<p>Estimates are from standardized Kaplan-Meier survival analyses, adjusted for all other factors shown in the table.</p>*<p>Diagnosis of HIV infection with or without a concurrent diagnosis of AIDS.</p><p>Dash indicates data not presented because the variance for the estimate is zero.</p
Percentage of IDUs with HIV diagnosis who did not progress to AIDS in 1996â2004, 33 U.S. States.
<p>Estimates are from standardized Kaplan-Meier analyses, adjusted for all other factors shown in the table. Data reported to CDC through June 2007. Dash indicates data not presented because the variance for the estimate is zero.</p